Methods and systems, including computer program products, for determining a plurality of color clusters based on a plurality of pixels associated with a color image, the clusters being fewer than the pixels. A grayscale value for each one of a plurality of points in a color space is determined. Each grayscale value is based on a weighted average of target differences between each point and the clusters. Each of the pixels is associated with one or more of the points. A grayscale value for each pixel is identified based on the grayscale value of the associated one or more points.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A computer-implemented method, comprising: determining, by computer, a plurality of color clusters based on a plurality of pixels associated with a color image, the clusters being fewer than the pixels; determining, by the computer, a grayscale value for each one of a plurality of points in a color space, each grayscale value based on a weighted average of target differences between each point and the clusters; associating, by the computer, each of the pixels with one or more of the points; and identifying, by the computer, a grayscale value for each pixel based on the grayscale value of the associated one or more points.
2. The method of claim 1 , where the identifying further includes: interpolating grayscale values of eight points in order to determine a grayscale value for a pixel.
3. The method of claim 1 , where: larger clusters are given greater weight in the weighted average of target differences.
4. The method of claim 1 , where: the color space is CIE L*a*b*.
5. The method of claim 1 , where: the points represent a subset of points in the color space.
6. The method of claim 1 , where: the points are a distribution of colors in the color space.
7. The method of claim 1 , further comprising: determining the target differences using a generalized sign-bit function.
8. The method of claim 7 , further comprising: receiving user input designating one or more hues in the color image as having a brighter or darker grayscale value.
9. The method of claim 1 , further comprising: scaling color components of each point before determining color differences.
10. The method of claim 1 , where: a cluster is a set of points in a color space.
11. A computer program product, encoded on a computer-readable medium, operable to cause data processing apparatus to perform operations comprising: determining a plurality of color clusters based on a plurality of pixels associated with a color image, the clusters being fewer than the pixels; determining a grayscale value for each one of a plurality of points in a color space, each grayscale value based on a weighted average of target differences between each point and the clusters; associating each of the pixels with one or more of the points; and identifying a grayscale value for each pixel based on the grayscale value of the associated one or more points.
12. The program product of claim 11 , where the identifying further includes: interpolating grayscale values of eight points in order to determine a grayscale value for a pixel.
13. The program product of claim 11 , where: larger clusters are given greater weight in the weighted average of target differences.
14. The program product of claim 11 , where: the color space is CIE L*a*b*.
15. The program product of claim 11 , where: the points represent a subset of points in the color space.
16. The program product of claim 11 , where: the points are a distribution of colors in the color space.
17. The program product of claim 11 , further comprising: determining the target differences using a generalized sign-bit function.
18. The program product of claim 17 , further comprising: receiving user input designating one or more hues in the color image as having a brighter or darker grayscale value.
19. The program product of claim 11 , further comprising: scaling color components of each point before determining color differences.
20. The program product of claim 11 , where: a cluster is a set of points in a color space.
21. A system comprising: means for determining a plurality of color clusters based on a plurality of pixels associated with a color image, the clusters being fewer than the pixels; means for determining a grayscale value for each one of a plurality of points in a color space, each grayscale value based on a weighted average of target differences between each point and the clusters; means for associating each of the pixels with one or more of the points; and means for identifying a grayscale value for each pixel based on the grayscale value of the associated one or more points.
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November 1, 2006
April 27, 2010
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